Chief Executive Leung Chun-ying may not have violated building rules by sealing an unauthorised room in one of his houses on The Peak a year ago, a veteran surveyor says.

Leung, who is at the centre of wide speculation on the existence of illegal structures in his two Peel Rise houses, revealed last week that he had built a brick wall to block off a 200 sq ft room that had been used as servants' quarters and for laundry.

The brick divider was unlikely to be a structural wall, based on a layout shown in a news report, said Vincent Ho Kui-yip, of the Institute of Surveyors.

"Leung did not reveal the exact location of the room, but according to the plan the wall functions like a partition," Ho said. "It was built inside the house and is not used as a retaining wall to protect the house from a slope, so it wouldn't have required permission from the Buildings Department."

He emphasised the validity of his judgment depended on the accuracy of the layout plan.

The plan, which Apple Daily drew up after it received a complaint, shows a wall separated a living room storage area on the lower ground floor from the 200 sq ft room, which had been built without authorisation.

Leung's houses contained six illegal structures, the department said in June after an inspection. On Friday, Leung issued a 14-page media statement making public four other unauthorised installations, including the room extension, in an attempt to clear the air over the controversy.

Leung said the extended area came to his attention in October last year, and he built the wall the next month to seal the room, and it had not been used since then.

Media reports have speculated he may be criminally liable for building that wall without the department's permission. It has also been reported - without substantial evidence - that an employee of the department raised queries about the wall during an inspection but was told by senior colleagues not to follow up on it.

Ho said if permission was not needed to build the wall, an outstanding issue now facing Leung was a possible department order requiring him to fill the extended area to avoid future reuse. "He would be prosecuted if he ignores the order," the surveyor said.

A former senior official of the department said any disagreement between junior and senior officers must be recorded, according to internal practice.

"One must give a sound reason for giving up an investigation and it will be written into a report," the person said, urging the department to clear public doubts over its integrity.

This article appeared in the South China Morning Post print edition as CY may be in clear on sealing room

The 'illegal structures' issue is a non-issue, created by inefficient government. If there was an efficient planning permission process, with reasonable time between application and approval, there would be no problem.